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That runner's high may translate into a lot of other long-lasting health benefits, a new report from an ongoing study suggests. Researchers have found that regular jogging, or any consistent aerobic exercise, in middle age and late in life may reduce people's risk of disabilities and help them live longer and healthier.

The study published this week in the Archives of Internal Medicine tracked two groups of people  "ever-runners" and "never-runners"  over two decades beginning in 1984. With her colleagues, lead author Dr. Eliza F. Chakravarty, an immunologist and rheumatologist at Stanford University School of Medicine, studied 538 people who run regularly, the majority of whom were selected from a national running club, along with a control group of 423 people who never run, drawn from the faculty and staff at Stanford. All participants were age 50 or older when the study began. Aside from their exercise habits, the two groups were demographically matched, similar in lifestyle habits, ethnicity and physical characteristics like weight. Each volunteer was asked to complete an annual questionnaire from 1985 through 2005 that traced their health status, including body mass index (a ratio of height to weight used to determine obesity), levels of disability and how much exercise they got.

Researchers analyzed the accumulated data at 8 years, 13 years and, most recently in 2005, the 21-year mark. Not surprisingly, the data showed that exercise was a boon to health. Over the years, compared with the never-exercisers, people who exercised regularly  in addition to running, activities included biking, aerobic dance and swimming  showed improved aerobic capacity, better cardiovascular fitness, increased bone mass, fewer inflammatory markers, less physical disability, better response to vaccinations and even improved thinking, learning and memory. They also lived significantly longer. What surprised researchers, however, was that those health differences persisted  survival and disability rates, in particular, continued to diverge for the two groups  over the course of the study. As the volunteers entered their seventh and eighth decades of life, many of the runners discontinued the activity and took up less strenuous activities like walking, but their health benefits endured. "We would have expected that as people got older, the difference between the two groups would start to narrow," Chakravarty says.

By year 19 of the study, 15% of the runners had died, compared with 34% of the non-running control group. Not only did fewer runners die of cardiovascular causes, but fewer died of other causes such as neurological and infectious disorders. At 21 years into the study, the authors reported, the running group experienced fewer disabilities in eight basic daily functions, including walking, eating, dressing, grip strength and routine physical activities  reporting, on average, one mild disability out of the eight. Never-runners recorded one to two disabilities on average, and were more likely to have a complete disability in one of those daily functions. Even as participants approach their 90s, the groups' disability and survival curves continue to diverge.

Although the study focused on runners, Chakravarty says, the benefits appear to accrue from any vigorous aerobic exercise. In fact, the data suggested that even a little bit of exercise was better than none. A few of the volunteers from the non-running group did break a sweat sometimes, if not in a prolonged, consistent way  they reported having run for more than one month at a time  and even that short period of regular aerobic exercise appeared to have created positive health benefits, Chakravarty says. For avid runners, more good news: the study found no significant difference between the condition of joints in pavement pounders and their more sedentary peers. Looking at X-rays and arthritis rates, Chakravarty says, "there was clearly no difference."

As more and more people survive longer and grapple with physical impairments, dementia and memory loss toward the end of life, it is important to preserve quality of life and functional abilities as long as possible, Chakravarty says. Her study suggests that regular aerobic exercise, even starting in middle age, could be a crucial factor. "It's never too late to start an exercise program," she says.